It is time to revisit X-ray. By enhancing, in the Near Field, Proximity X-ray Lithography (PXL), the technique is demonstrated that extends to 15nm printed feature size with 2:1 ratio of pitch to line width. "Demagnification by bias" of clear mask features is positively used in Fresnel diffraction together with rapid, multiple exposures of sharp peaks. Pitch is kep small by multiple, stepped exposures of the intense image followed by single development. The optical field is kept compact at the mask. Since the mask-wafer gap scales as the awaure of the mask feature size, mask feature sizes and mask-wafer gaps are comparatively large. A Critical Condition has been identified which is typically used for the highest resolution. Many devices, including batches of microprocessors, have been demonstrated previously by traditional 1X PXL which is the most mature of the Next Generation Lithographies and which is now further extended. Throughput and cost are conventional.
By using the Near Field in Proximity X-ray Lithography (PXL), the technique is demonstrated that extends beyond a resolution of 25 nm print featuer size with 2:1 pitch to line width. "Demagnification by bias" of clear mask features is positively used in Fresnel diffraction together with multiple exposures of sharp peaks. Exposures are performed without lenses or mirrors between mask and wafer, and the "demagnification" is achieved in the selectable range 1X to 9X. Pitch is kept small by multiple, stepped exposures of sharp, intense, image peaks followed by single development. Low pitch nested lines are demonstrated. The optical field is kep compact at the mask. Since the mask-wafer gap scales as the square of the mask feature size, mask feature sizes and mask-wafer gaps are comparatively large. Because the features are themselves larger, the masks are more easily manufactured. Meanwhile exposure times, for development levels high on sharp peaks, are short, and there are further benefits including defect reduction. Many devices, including batches of microprocessors, have been demonstrated previously by traditional 1X PXL which is the most mature of the Next Generation Lithographies and which is now further extended. For 2D Near field patterning, temporal and spatial incoherence at the Critical Condition are used to show, not only that peculiarities in the aerial pattern, such as "ripple" and "bright spots", can be virtually eliminated, but also that there is an optimum demagnification, around 3X, in the Fresnel diffraction, where the contrast is highest. At this demagnification, patterns of various dimensions can be printed using various and appropriate demagnifications.
The ability to produce fine features using X-ray proximity lithography is controlled predominantly by diffraction and photoelectron blur. The diffraction manifests itself as feature 'bias.' The classical approach is to attempt to minimize the bias; that is, to print features which are 1:1 images of those on the mask. However, bias can also be exploited to print features smaller than those on the mask. This demagnification-by-bias technique can be optimized with respect to mask-wafer gap and resist processing, and can provide reductions of 3X to 6X. Demagnification offers many of the same advantages as projection optical lithography in terms of critical dimension control: relaxed mask features CD. In addition, it provides a very large 'depth of focus' and wide dose latitude. In consequence proximity X-ray lithography is extendible to feature sizes below 25 nm, taking advantage of comparatively large mask features (> 0.1 nm) and large gaps (10 -25 micrometer). The method was demonstrated for demagnification values down to X3.5. To produce DRAM half- pitch fine features techniques such as multiple exposures with a single development step are proposed.
Advances in today's semiconductor industry have been achieved mainly by decreasing the minimal feature size thereby increasing the complexity of the devices. Lithography tool shave to provide for high resolution and large depth of focus. X-ray lithography offers promising solutions and is currently an actively researched area.
Chemically amplified deep UV photoresist is well known with its sensitivity towards base contaminants either from track and stepper ambience or from substrate. The former gives 'T- top' formation whereas the latter leads to 'footing' in line pattern. This sensitivity originates from the chemically amplification nature that uses photoacid to catalyze the deprotection of resin. To overcome environmental unstability, a variety of chemically stable resists have been formulated. However, during evaluation of some of these new deep UV photoresist, 'bottom pinching' (BP) effect was observed for photoresist on top of organic bottom anti-reflection coating (BARC). BP effect is the slimming of photoresist line immediately above the substrate, which shows the photoresist actually dissolutes at a higher rate near the substrate. This might be caused by higher concentration of acid in the photoresist near the substrate. It is believed that the excess amount of acid diffuses out from the BARC layer. Thus, the softbake of BARC and photoresist, the post-exposure bake of photoresist are to be optimized for the 'bottom pinching' effect.
Decreasing dimensions in integrated circuits impose increasing demands in processing. Among requirements are reduced resistance in interconnects on high density chips and also low leakage currents. Transmission electron microscopy has been used to study the microstructures associated with salicide interconnects in wafers prepared on design rules between 0.6 to 0.35 microns. Irregularities such as varying gate width, interconnects in wafers prepared on design rules between 0.6 to 0.35 microns. Irregularities such as varying gate width, intergrowths of poly-silicon and polycrystallinity in titanium silicide were observed. Precipitation has not so far been noticed in pure or doped silica insulating layers.
The embryonic area of interventional MRI, i.e. interstitial therapy under MR guidance, includes deep tissue laser ablation of lesions. Laser fibers can be located inside lesions by first inserting an MR-compatible cannula into the lesion and then inserting the laser fiber through the cannula into the lesion. Two factors are critical in selecting alloys for cannulae: the material should exhibit so little magnetic susceptibility that it will neither distort the MR image nor torque even at high field strengths, yet it should exhibit enough susceptibility defect that the cannula can be visualized by MR during positioning. Wires of metals and alloys were tested in a magnetometer to measure their magnetic moment, and imaged with spin echo and gradient echo MRI. Direct measurement of magnetic moment was a good indicator of MR- compatibility. Artifacts visualized with spin echo pulse sequences were smaller than those produced with gradient echo sequences.